New Delhi: Originally predicted in the early 20th century by Albert Einstein, gravitational waves – ripples in space and time – were not detected until 2015, when the Laser Interferometer Gravitational-wave Observatory (LIGO) identified the first such signal from two merging black holes.

On Wednesday, scientists announced the detection of a fourth gravitational wave signal coming as a result of the merger of two black holes.

It’s the first time this phenomenon has been measured simultaneously by both the US-based LIGO and Italy-based Virgo detectors.

The first direct evidence of gravitational waves was detected in February 2016.

LIGO’s two detectors, located in Livingston, Louisiana, and Hanford, Washington, later detected two other similar events, Xinhua reported.

The latest observation was made on August 14, 2017. It’s the first gravitational wave signal recorded by the Virgo detector.

“Today, we are delighted to announce the first discovery made in partnership between the Virgo Gravitational-Wave Observatory and the LIGO Scientific Collaboration, the first time a gravitational-wave detection was observed by these observatories, located thousands of miles apart,” said France Cordova, Director of the US National Science Foundation, which funded the LIGO project.

“This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe,” Cordova added.

The detected gravitational waves were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the Sun and located about 1.8 billion light-years away, researchers said.

The newly produced spinning black hole has about 53 times the mass of our Sun, which means that about three solar masses were converted into gravitational-wave energy during the coalescence, they said.

A paper about the event has been accepted for publication in the journal Physical Review Letters.

The Virgo collaboration, which joined in the LIGO’s observation on August 1, consists of more than 280 physicists and engineers belonging to 20 different European research groups.

Here are some things about gravitational waves you should know:

Gravitational waves are ripples that travel at the speed of light through the fabric of space-time.

Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years.

On February 11, 2016, physicists from the Laser Interferometer Gravitational-wave Observatory (LIGO) announced that they had detected gravitational waves from a black hole collision, proving Einstein was right. The LIGO detections represent a much-awaited first step toward opening a whole new branch of astrophysics
Prior to the direct detection of gravitational waves, there was indirect evidence for their existence. For example, measurements of the Hulse–Taylor binary system suggest that gravitational waves are more than a hypothetical concept.

The historic detection of gravitational waves may open a new era of astronomy in which gravitational waves are tools for studying the most mysterious and exotic objects in the universe.